Macro-Assisted Multi-Connectivity Scheme in Multi-RAT Cellular Systems

ABSTRACT

A novel Macro-assisted Multi-Connectivity (MC) mobility scheme for UEs traversing clusters of (mmWave) small cells (small-BS or SBS) under the coverage of the same 5G or LTE Macro-cell (macro-BS or MBS) is proposed. It keeps the same Control/User split scheme and C-Plane anchor at MBS, same as in LTE Dual Connectivity (DuCo or DC), yet extending DuCo with a multi-connectivity split bearer user plane. For example, MBS adopts a multi-way packet data convergence protocol (PDCP) bearer split based on routing weighted by channel quality, SBS&#39;s resource availability, etc. with or without inter-BS flow control. Utilizing the MC user plane, a macro-assisted make-before-break MC mobility can be enabled.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation, and claims priority under 35 U.S.C.§ 120 from nonprovisional U.S. patent application Ser. No. 15/099,708,entitled “A Macro-assisted Multi-connectivity Scheme in Multi-RATCellular Systems,” filed on Apr. 15, 2016, the subject matter of whichis incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communications,and, more particularly, to macro-assisted multi-connectivity schemes inmulti-RAT wireless systems.

BACKGROUND

A Long-Term Evolution (LTE) system offers high peak data rates, lowlatency, improved system capacity, and low operating cost resulting fromsimplified network architecture. LTE systems also provide seamlessintegration to older wireless network, such as GSM, CDMA and UniversalMobile Telecommunication System (UMTS). In LTE systems, an evolveduniversal terrestrial radio access network (E-UTRAN) includes aplurality of base stations, such as evolved Node-B's (eNBs)communicating with a plurality of mobile stations referred as userequipment (UEs). Dual Connectivity (DuCo or DC) UE is introduced toenhance mobility, bandwidth, and flexibility use of the network. A UEwith dual connectivity has more than one transceivers corresponding tomore than one MAC entities. The multiple MAC entities can be configuredto communicate with multiple eNBs simultaneously.

The upcoming next generation “5G” Millimeter Wave (mmWave) small cell isexpected to coexist with microwave (e.g., E-UTRAN) macro cells for along time. The macro-assisted mmWave cellular systems exploit the factthat mmWave small cells and microwave macro cells may compensate eachother very well in coverage area, link capacity, spectrum availability,and service robustness. From both network and radio access'sperspectives, mmWave is currently considered a very promising choice forin-door or out-of-door “5G” cellular small cells, which may compensatemicrowave macro-cell in shortage of spectrum or in need for economicalhigh-speed data services. In particular, the small cells offer downlink(DL) throughput boosting or coverage extension for an umbrellamacro-cell at its edge. On the other hand, macro-cell coverage makes upmmWave's directional coverage limitation and bursty link disruption byoffering reliable omni-directional overlay services for time-critical ormission-critical control signaling, or offering more robust and seamlessservices for low-rate high-mobility (voice) users. Together theyconstitute a layered or scalable communication infrastructure thatpromise reliability, wide coverage, economical yet diversified mobileQoS services.

The existing LTE HetNet Dual Connectivity (DuCo) architecture is notfine-tuned for mmWave small cells that have new radio characteristicsand face new 5G requirements as well. The LTE DuCo architecture isdesigned only for some less densely deployed, relatively low-frequencymicrowave smallcell scenarios, and not optimized for stationary or densescenarios with Gbps mmWave small cells. Furthermore, LTE DuCo mobilityis used in omni-directional cellular systems of no beamformed controlchannel. While LTE DuCo may be used as the baseline for macro-assistedmmW mobility, it lacks some reliability due to beamforming. With UE'scontrol channel anchored solely to master eNB (MeNB), DuCo allows 2-wayPDCP bearer split between MeNB and secondary eNB (SeNB) for data planeto UE. UE sees service degradation at the edge due to signal weakness orfrequent (beamformed) link disruption during S2S addition/release orotherwise rate mismatch during S2M fallback. Similar 2-way split DuCoconcepts are applied to other Multi-RAT systems, e.g., LTE-WiFi (LWA)aggregation, with potentially the same limitation.

Compared to 4G system, 5G demands uniform UE service experience even at“cell edge”, while 5G mmWave-specific CH and BF characteristics presentnew challenges to mobility reliability and seamlessness. First,directional beamforming makes mobility management even harder and moretime critical due to complex, time-consuming beam alignment, beamswitching, and beam tracking. Second, Multiple levels of beams, multiplebeams per level, multiple (TDM) BF-ed control beams per cell to scanmakes scanning more time and power consuming with frequent andintermittent link disruptions and blockage. Third, high handover (HO)ping-pong rate happens even at mild channel blocking while HO failurerate is very high at severe blockage. The service rate and reliabilityat cell edges of 5G multi-RAT systems, if still following the existingdesign of DuCo's data plane, may not meet the 5G requirements foruniform edge or center services. For this purpose and for the purpose ofproviding more robust mobility, a bandwidth aggregation at the cell edgeof neighboring small cells and/or macrocell, and a make-before-breakmobility scheme, may present a whole solution. Such a design is not yetsupported by the DuCo architecture in either user plane or controlplane. Therefore, an enhanced macrocell-assisted smallcell mobility withmulti-connectivity, for example for a multi-RAT system including 5Genhanced LTE macro plus (mmWave) smallcell systems, or for a LTE-WiFiaggregation systems, is desired to meet both the 5G demands and themmWave mobility challenges.

SUMMARY

A novel Macro-assisted Multi-Connectivity (MC) scheme for fixed userequipments (UEs) connecting to or mobile UEs traversing clusters of(mmWave) small cells (small-BS or SBS) under the coverage of the same 5Gor LTE Macro-cell (macro-BS or MBS) is proposed. It keeps the sameControl/User split scheme and C-Plane anchor at MBS, same as in LTE DualConnectivity (DuCo or DC), yet extending DuCo with a multi-connectivitysplit bearer user plane. For example, MBS adopts a multi-way packet dataconvergence protocol (PDCP) bearer split based on routing weighted bychannel quality, SBS's resource availability, etc. with or withoutinter-BS flow control. Utilizing the MC user plane, a macro-assistedmake-before-break MC mobility can be enabled.

In one embodiment, a UE establishes a radio resource control (RRC)connection with a macro base station (MBS) in a heterogeneous networkhaving a macrocell served by the MBS and overlaying smallcells serviceby smallcell base stations (SBSs). The UE establishes amulti-connectivity (MC) multi-way split bearer U-Plane for simultaneousdata transmission with one or more base stations. The UE performsmacro-assisted make-before-break MC mobility by using the multi-waysplit bearer.

In another embodiment, a macro base station (MBS) establishes a radioresource control (RRC) connection with a UE in a multi-RAT networkhaving a microwave macrocell served by the MBS and overlaying smallcellsserved by smallcell base stations (SBSs). The MBS establishes amulti-connectivity (MC) multi-way split bearer U-Plane together with theSBSs for providing simultaneous data transmission to the UE. The MBSperforms macro-assisted make-before-break MC mobility for the UE byusing the multi-way split bearer.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 illustrates a macro-assisted multi-connectivity scheme in aheterogeneous network (HetNet) having a macrocell and overlappingMillimeter Wave (mmWave) smallcells in accordance with one novel aspect.

FIG. 2 illustrates a macro-assisted make-before-break multi-connectivity(MC) mobility utilizing MC split bearer user plane in accordance withone novel aspect.

FIG. 3 is a simplified block diagrams of macrocell base station (MBS),smallcell base stations (SBS), and a user equipment (UE) that carrycertain embodiments of the present invention.

FIG. 4 is a simplified block diagram of a user equipment (UE) that carrycertain embodiments of the present invention.

FIG. 5 illustrates a weighted multi-connectivity (MC) split bearer fromprotocol layers in different base stations (MBS and SBS) with anembodiment of a 3-way UL split bearer.

FIG. 6 illustrates one embodiment of a macro-assisted make-before-breakmobility process with multi-connectivity (MC) by using multi-way splitbearer.

FIG. 7 illustrates a first example of a message flow formulti-connectivity SBS addition by an embodiment of forming 3-waysimultaneous connectivity with one MeNB and two SeNB's.

FIG. 8 illustrates a second example of a message flow formulti-connectivity SBS modification or release by an embodiment ofswitching from 3-way split bearer to 2-way split bearer.

FIG. 9 is a flow chart of a macro-assisted multi-connectivity schemefrom UE perspective in multi-RAT cellular systems in accordance with onenovel aspect.

FIG. 10 is a flow chart of a macro-assisted multi-connectivity schemefrom network perspective in multi-RAT cellular systems in accordancewith one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates a macro-assisted multi-connectivity scheme in aheterogeneous network (HetNet) 100 having a microwave macrocell andoverlapping Millimeter Wave (mmWave) smallcells in accordance with onenovel aspect. HetNet 100 comprises a macro base station MBS 101, a firstsmallcell base station SBS1 102, a second smallcell base station SBS2103, a user equipment UE 104, and a serving gateway SGW 105. FIG. 1illustrates a multi-connectivity (MC) mobility scheme for macro-assistedlow to medium UE mobility across a cluster of mmWave smallcells underthe same macrocell coverage.

In accordance with a first novel aspect, macro-assisted and UEintelligent HetNet mobility is provided. A novel end-to-endMulti-Connectivity (MC) scheme for U-Plane make-before-break mobility ormulti-cell bandwidth (BW) aggregation for the purpose of edgelessuniform UE performance and seamless mobility services. This BWaggregation is at PDCP layer bundling multiple SBS's U-plane resourceswith MBS's U-plane resource for the same UE under their coverage. Inaccordance with a second novel aspect, a dynamic weight-based U-planeconfiguration of 2-way, 3-way, or multi-way split bearer is provided. Anovel definition of split bearer and a novel control flow to set up ortear down sub-bearer, adapt the load split onto each sub-bearer inweighted manner based on any existing scheduling algorithm and one orall of the following (non-limiting) weighting factors: 1) the real-timechannel quality of its radio link; 2) SBS's available resources (bufferstatus, X2 link quality) and other flow control variables of eachsub-bearer; 3) UE mobility states; and 4) smallcell addition or releasestatus (based on independent target SBS selection schemes).

In one example, MBS 101 adopts a 3-way or multi-way PDCP bearer splitwith SBS1 102 and SBS2 103 based on scheduling and routing weighted bythe list of weighting factors with or without inter-BS flow control. UE104 establishes multiple connections with MBS 101, SBS1 102, and SBS2103 (e.g., CH, CH1, and CH2, respectively). Optionally, the UE provideschannel quality of its radio links to the MBS as depicted by arrow 121,while the SBSs provide their resource status to the MBS as depicted byarrow 122 to enable the MBS making dynamic scheduling and routingdecisions. In the downlink (DL), PDCP layer traffic flows through SGW105 to MBS 101, and is then scheduled by the MBS to flow to the UEdirectly, or through SBS1 102 and/or SBS2 103 and then to the UE. In theuplink (UL), PDCP layer traffic is routed by MBS 101 from the UE to theMBS and the SGW directly, or through SBS1 and/or SBS2 and then to theMBS and the SGW.

FIG. 2 illustrates a macro-assisted make-before-break multi-connectivity(MC) mobility utilizing MC split bearer user plane in HetNet 200 inaccordance with one novel aspect. HetNet 200 comprises a mobilitymanagement entity MME, a serving gateway SGW, a macrocell base stationMBS, three smallcell base stations SBS1, SBS2, and SBS3, and a userequipment UE. In the example of FIG. 2, the UE is connected to multiplebase stations in data plane (MBS, SBS1, and SBS2 via Uu-U) through asingle multi-way PDCP bearer simultaneously, but is anchored orconnected to the MBS only in RRC control plane (via Uu-C(RRC)). The UEmonitors and reports dynamic channel states to the MBS for network-siderouting or scheduling decision of loading traffic onto differentsub-bearers of the multi-way split bearer. Given the RRM informationbetween UE-SBS(s), the MBS can follow process to handle SBS addition,release, modification and change to achieve macro-assisted mobility withMC when UE moves across a cluster of smallcells under the same macrocellcoverage.

FIG. 3 is a simplified block diagrams of macrocell base station (MBS),two smallcell base stations (SBS1 and SBS2), and a user equipment (UE)that carry certain embodiments of the present invention. In the exampleof FIG. 3, the MBS comprises MAC, RLC, and PDCP protocol layers and aPDCP handler 311 for routing/flow control with weighting. SBS1 and SBS2each comprises MAC and RLC protocol layer entities. The UE comprisesmultiple entities for MAC and RLC protocol layers and a PDCP handler 321for PDCP packets reordering. The multi-connectivity 3-way split bearerincludes one MCG sub-bearer, one SCG1 sub-bearer, and one SCG2sub-bearer in the U-plane. Through PDCP handler 311, the MBS collectsdynamic channel states for making a routing or a scheduling decision ofloading traffic onto different sub-bearers of the 3-way split bearer.The UE adopts the dynamic weighted based U-plane routing and schedulingfor the 3-way split bearer. In the downlink, the UE reorders PDCP layerpackets via PDCP hander 321 for a single downlink flow that arrives atthe UE from one or more base stations (MBS, SBS1, and SBS2). In theuplink, the UE splits PDCP layer packets for a single uplink flow thatis destined to the MBS directly or through SB1 and/or SBS2.

FIG. 4 is a simplified block diagram of a user equipment (UE 401) thatcarry certain embodiments of the present invention. UE 401 has anantenna (or antenna array) 414, which transmits and receives radiosignals. A RF transceiver module (or multi-RF modules) 413, coupled withthe antenna, receives RF signals from antenna 414, converts them tobaseband signals and sends them to processor 412 via baseband module (ordual BB modules) 415. RF transceiver 413 also converts received basebandsignals from processor 412 via baseband module 415, converts them to RFsignals, and sends out to antenna 414. Processor 412 processes thereceived baseband signals and invokes different functional modules toperform features in UE 401. Memory 411 stores program instructions anddata to control the operations of UE 401.

UE 401 also includes a 3GPP protocol stack module 426 supporting variousprotocol layers including NAS 425, AS/RRC 424, (multi-)PDCP/RLC 423,(multi-)MAC 422 and PHY 421, a TCP/IP protocol stack module 427, anapplication module APP 428, and a management module 430 including aconfiguration module 431, a mobility module 432, a control module 433,and a data handling module 434. The function modules, when executed byprocessor 412 (via program instructions and data contained in memory411), interwork with each other to allow UE 401 to perform certainembodiments of the present invention accordingly. Configuration module431 obtains U-plane setup preference information, mobility circuit 432determines UE mobility, control circuit (C-Plane handler) 433 determinesand applies a preferred U-plane setup for the UE dynamically, anddata-handling circuit (U-Plane handler) 434 performs correspondingU-path setup activation, selection, and packet data transferring.

FIG. 5 illustrates a weighted multi-connectivity (MC) split bearer fromprotocol layers in different base stations (MBS and SBS1 and SBS2) withan embodiment of a 3-way UL split bearer. Each base station comprisesPDCP, RLC and MAC sublayers. The MBS considers UE's RRM measurementreports to decide whether or when to set up MC mobility with 3-way PDCPsublayer PDU TX routing and RX reordering. The UE learns the smallcellSBS and bearer addition, release, change, modification still with itscontrol plane anchored only at the MBS. The MBS adapts the load orroutes traffic onto the split bearer based on real-time feedback ofradio quality (for each channel) with each involved SBS, using weightedfair queueing for example, until it realizes that it may have to changethe bearer from 2-way to 3-way or vice versa.

FIG. 6 illustrates one embodiment of a macro-assisted make-before-breakmobility process with multi-connectivity (MC) by using multi-way splitbearer in a HetNet 600. HetNet 600 comprises a mobility managemententity MME, a serving gateway SGW, a macrocell base station MBS, threesmallcell base stations SBS1, SBS2, and SBS3, and a user equipment UE.The UE moves across the mmWave smallcells under the same macrocellcoverage. Initially, the UE establishes a radio resource control (RRC)connection with the MBS for C-plane. The UE is located near SBS1 andestablishes a multi-connectivity (MC) 2-way split bearer U-plane forsimultaneous data transmission with both MBS and SBS1.

At time t0 as depicted in (a), UE moves away from SBS1 towards SBS2. MBSlearns it from the control plane connection signaling, e.g., RRM reportsfrom the UE. MBS predicts that SBS2 (not SBS3) to be potential target.At time t1 as depicted in (b), MBS helps to establish UE-SBS2 dataconnection while possibly maintaining UE-SBS1 connection by adopting theweighted (3-way or N-way) multi-connectivity bearer split, with sharesof traffic routed towards each SBS in proportion to their weightingfactors. For example, by following any channel-independent scheduling,e.g., weighted fair queueing or proportional fairness scheduling. In themeanwhile, MBS decides to request resources from the SBS1 or SBS2 ofcertain amount, so that the QoS for the respective E-RAN is guaranteedby the exact sum of resources provided by the MBS and the SBS(s)together, or even more. At time t2 as depicted in (c), when UE movesfurther away from SBS1, based on channel reports, MBS disconnectsUE-SBS1 connection, and directs all data to UE-SBS2 connection, i.e.,changing the 3-way split bearer to 2-way split bearer.

In legacy LTE mobility or LTE DuCo, break-before-make mobility scheme isa common practice, with which a UE initially connected to a single(small cell) base station breaks the existing connection before it canmake or connect to another neighboring small cell. In other words, theUE will not communicate with two small cell base stations particularlyin user plane simultaneously. By “make-before-break”, the proposed MCscheme is making/setting up the connection with another neighboring SBSwithout breaking/disconnecting with the existing one, all under theumbrella of the MBS coverage and with the signaling and control supportof MBS. In the embodiment of macro-assisted small cell mobility, theproposed multi-connectivity (MC) mobility enables one UE to connect andcommunicate with two or more small cell base stations simultaneously, aselaborated by the control-plane end-to-end signaling support for SBSaddition/release/modification, UE-MBS channel measurement and inter-BSexchange for flow control, and user-plane PDCP-layer multi-way splitbearer supported by BS's and UE. By allowing a UE connecting to two ormore SBSs at the same time, the MC scheme enables BW aggregation at thecell edge and more seamless handover between SBSs.

FIG. 7 illustrates a first example of a message flow formulti-connectivity SBS addition by an embodiment of forming 3-waysimultaneous connectivity with one MeNB and two SeNB's. The example ofFIG. 7 corresponds to the example of FIG. 6 when UE moves from time t0to time t1. The UE is connected to MBS and SBS1, and is moving towardSBS2. As a result, SBS2 can be added by a 3-way split bearer at MBS(with SBS1 and SBS2), with modifications to MBS, SBS1, and SBS2. In step711, UE sends a measurement report of radio link quality to MBS. In step712, SBS1 and SBS2 sends their available resources and other flowcontrol variables to MBS. In step 713, MBS makes MC rounding decision:to calculate MC split bearer E-RAB QoS parameters for SBS1 andto-be-added SBS2 based on weights (RRM, resource, etc.). In step 721,MBS sends an SBS addition request to SBS2, carrying SCG configurationinformation, with the E-RAB parameters for the 3-way MC split bearer. Instep 722, SBS2 makes RRM decision: admitting resources for the MC splitbearer and allocating L1 and L2, and providing dedicated RACHconfiguration for synchronization. In step 723, SBS2 sends an SBSaddition request acknowledge back to MBS, carrying SCG configuration. Instep 731, MBS sends an SBS modification request to SBS1, with MC splitbearer E-RAB QoS. In step 732, SBS1 replies with an SBS modificationrequest acknowledgement. In step 741, UE receives a RRC connectionreconfiguration from MBS, carrying MC bearer update information. In step742, UE sends a RRC connection reconfiguration complete to MBS. In step743, MBS sends an SBS modification confirm to SBS1. In step 744, UEperforms random access procedure with SBS2 for synchronization. In step751, MBS sends serial number status transfer to SBS2. In step 752, MBSmakes MC weighted routing decision for PDCP PDUs and forwards data toSGW, SBS1, and SBS2. In step 753, UE changes its E-RAB split bearer to3-way, and continue PDCP RX reordering. Finally, in step 761, MBSperforms path update procedure: 3-way MC split bearer E-RAB modificationprocess, involving both SGW and MME.

FIG. 8 illustrates a second example of a message flow formulti-connectivity SBS modification or release by an embodiment ofswitching from 3-way to 2-way split bearer. The example of FIG. 8corresponds to the example of FIG. 6 when UE moves from time t1 to timet2. When UE is moving further away from SBS1, the 3-way MC split bearer(between MBS, SBS1, and SBS2) is converted to a 2-way MS split bearer(between MBS and SBS2) by releasing SBS1 and modifying E-RAB bearer forUE, MBS, and SBS2. In step 811, UE sends a measurement report of radiolink quality to MBS. In step 812, SBS1 and SBS2 sends their availableresources and other flow control variables to MBS. In step 813, MBSmakes MC rounding decision: to re-calculate MC split bearer E-RAB QoSparameters for removing SBS1, and change 3-way to 2-way MC split bearer.In step 821, MBS sends a SeNB modification request to SBS2, withmodified MC split bearer E-RAB QoS. In step 822, SBS2 makes RRMdecision: modify its E-RAB QoS for the split bearer and continueresource and flow control update with MBS. In step 823, SBS2 sends aSeNB modification request acknowledge back to MBS. In step 831, MBSsends an SBS release request to SBS1. In step 832, SBS1 replies with anSBS release response. In step 841, UE receives a RRC connectionreconfiguration from MBS, carrying MC bearer update information. In step842, UE sends a RRC connection reconfiguration complete to MBS. In step843, SBS1 sends SN status transfer to MBS. In step 844, MBS sends SNstatus transfer to SBS2. In step 845, MBS sends SeNB reconfigurationcomplete to SBS2. In step 846, MBS sends SeNB modification confirm toSBS2. In step 852, MBS makes MC weighted routing decision for PDCP PDUs.In step 853, MBS sends end marker packet to SBS1. In step 854, MBSforwards data to SGW and SBS2. In step 855, UE changes its E-RAB splitbearer to 2-way, and continue PDCP RX reordering. Finally, in step 861,MBS performs path update procedure: 3-way MC split bearer E-RABmodification to become 2-way MC split bearer, involving SGW and MME, andsend E-RAB modification indication. In step 862, bearer modification isperformed between SGW and MME. In step 863, MBS receives E-RABmodification confirmation. In step 864, MBS sends UE context release toSBS1.

There are multiple possible variants to the present invention ofmacro-assisted MC mobility scheme. It applies to one LTE or evolved LTEmacro-BS plus multiple mmWave small cells or any other small cell RATS,e.g., any 3GPP RAT technologies. The MC scheme can be extended tosimilar 3GPP schemes such as eLWA or LWA (LTE/WLAN aggregation), whereWi-Fi AP or Wi-Fi termination (WT) is acting like a smallcell, whilemacrocell is LTE eNB, with PDCP-layer DuCo like 2-way LWA split bearer,switched LWA bearer, or LWA bearer corresponding to DuCo split bearer.The exemplary changes between 2-way and 3-way bearer split (or splitbearer) can be extended to N-way, where integer N can be larger than 3,by following the same mechanism. The MC scheme can be extended to otherlayers of 3-way or N-way multi-connectivity for one MBS and multipleSBSs talking to the same UE at the same time, as long as the weightedflow splitting and make-before-break mobility scheme are followedsimilarly. It applies to non-mobility MC scheme as well. The messagingand control flow in MC SBS addition/modification/release plots may berevised with shuffled steps, more or less information elements, etc.,but still follow the same logic as defined. The messaging and controlflow in MC SBS addition/modification/release plots may be extendedsimilarly to other scenarios, including MBS-to-MBS handover with eachMBS has two or more serving SBS's for the same UE in its coverage.Duplicate or different PDUs from the same flow but through multiple datapaths (by different SBSs). Dynamic weight based routing or 2-way, ormulti-way (N-way) MC split bearer configuration of its E-RAB QoSparameters can split same-flow PDCP traffic onto each sub-bearer (thatcorresponds to different SBS for the same split bearer). While therouting can be based on any existing scheduling algorithms and one orall of the following (non-limiting) weighting factors: 1) the real-timechannel quality of UE-sensed radio link, e.g, RSRP, RSRP, etc., fromeach MBS or SBS; 2) SBS's available resources (buffer), X2 or radio linkquality, or other Flow Control variables for each sub-bearer; and 3) UEmobility states; small cell addition/release status (based onindependent target SBS selection schemes).

FIG. 9 is a flow chart of a macro-assisted multi-connectivity schemefrom UE perspective in multi-RAT cellular systems in accordance with onenovel aspect. In step 901, a UE establishes a radio resource control(RRC) connection with a macro base station (MBS) in a Heterogeneousnetwork having a macrocell served by the MBS and overlaying smallcellsservice by smallcell base stations (SBSs). In step 902, the UEestablishes a multi-connectivity (MC) multi-way split bearer U-Plane forsimultaneous data transmission with one or more base stations. In step903, the UE performs macro-assisted make-before-break MC mobility byusing the multi-way split bearer.

FIG. 10 is a flow chart of a macro-assisted multi-connectivity schemefrom network perspective in multi-RAT cellular systems in accordancewith one novel aspect. In step 1001, a macro base station (MBS)establishes a radio resource control (RRC) connection with a UE in amulti-RAT network having a microwave macrocell served by the MBS andoverlaying mmWave smallcells served by smallcell base stations (SBSs).In step 1002, the MBS establishes a multi-connectivity (MC) multi-waysplit bearer U-Plane together with the SBSs for providing simultaneousdata transmission to the UE. In step 1003, the MBS performsmacro-assisted make-before-break MC mobility for the UE by using themulti-way split bearer.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method comprising: establishing a radioresource control (RRC) connection with a master node by a user equipment(UE) in a multi-Radio Access Technology (RAT) network having one cellserved by the master node and other cells served by one or moresecondary nodes; establishing multi-connectivity (MC) multi-way splitbearers for simultaneous data transmission with one or more nodes; andperforming inter-node mobility by using the split bearers, wherein theinter-node mobility involves switching between (N−1)-way and N-way ofeach split bearer, wherein N is an integer that is greater than one. 2.The method of claim 1, wherein UE monitors and reports dynamic channelstates to the master node for a routing or a scheduling decision ofloading traffic onto different Radio Link Control (RLC)-bearers of thesplit bearers.
 3. The method of claim 1, wherein the UE reorders PacketData Convergence Protocol (PDCP) layer Protocol Data Units (PDUs) foreach single downlink radio bearer that arrives at the UE from one ormore nodes.
 4. The method of claim 1, wherein the UE splits Packet DataConvergence Protocol (PDCP) layer Protocol Data Units (PDUs) for eachsingle uplink radio bearer through one or more nodes.
 5. The method ofclaim 1, wherein the UE adopts a dynamic weighted based U-plane routingand scheduling for the split bearers.
 6. The method of claim 1, whereinthe inter-node mobility involves a Radio Link Control (RLC) bearerswitching for each split bearer, wherein the RLC bearer switching isbased on channel quality, resource availability, network policy, UEpreference, and traffic loads, and wherein the RLC bearer switching isperformed by RLC bearer release, addition, and modification.
 7. Themethod of claim 1, wherein the UE uses the split bearers to aggregatemulti-cell bandwidth for Packet Data Convergence Protocol (PDCP) layerProtocol Data Units (PDUs) from each radio bearer but through differentnodes.
 8. A User Equipment (UE) comprising: a control plane handlingcircuit that establishes a radio resource control (RRC) connection witha master node in a multi-Radio Access Technology (RAT) network havingone cell served by the master node and other cells served by one or moresecondary nodes; a user plane handling circuit that establishesmulti-connectivity (MC) multi-way split bearers for simultaneous datatransmission with one or more nodes; and a mobility circuit thatperforms inter-node mobility by using the split bearers, wherein theinter-node mobility involves switching between (N−1)-way and N-way ofeach split bearer, wherein N is an integer that is greater than one. 9.The UE of claim 8, wherein UE monitors and reports dynamic channelstates to the master node for a routing or a scheduling decision ofloading traffic onto different Radio Link Control (RLC)-bearers of thesplit bearers.
 10. The UE of claim 8, wherein the UE reorders PacketData Convergence Protocol (PDCP) layer Protocol Data Units (PDUs) foreach single downlink radio bearer that arrives at the UE from one ormore nodes.
 11. The UE of claim 8, wherein the UE splits Packet DataConvergence Protocol (PDCP) layer Protocol Data Units (PDUs) for eachsingle uplink radio bearer through one or more nodes.
 12. The UE ofclaim 8, wherein the UE adopts a dynamic weighted based U-plane routingand scheduling for the split bearers.
 13. The UE of claim 8, wherein theinter-node mobility involves a Radio Link Control (RLC) bearer switchingfor each split bearer, wherein the RLC bearer switching is based onchannel quality, resource availability, network policy, UE preference,and traffic loads, and wherein the RLC bearer switching is performed byRLC bearer release, addition, and modification.
 14. The UE of claim 8,wherein the UE uses the split bearers to aggregate multi-cell bandwidthfor Packet Data Convergence Protocol (PDCP) layer Protocol Data Units(PDUs) from each radio bearer but through different nodes.
 15. A methodcomprising: establishing a radio resource control (RRC) connection witha user equipment (UE) by a master node in a multi-RAT network having onecell served by the MN and other cells served by secondary nodes;establishing multi-connectivity (MC) multi-way split bearers togetherwith the secondary nodes for providing simultaneous data transmission tothe UE; and performing inter-node mobility for the UE by using the splitbearers, wherein the MN supports secondary node addition or removal fromthe split bearers through a radio access network (RAN) and a corenetwork signaling to enable bearer splitting or merging.
 16. The methodof claim 15, wherein the MN collects dynamic channel states for making arouting or a scheduling decision of loading traffic onto different RadioLink Control (RLC)-bearers of the split bearers.
 17. The method of claim15, wherein the MN exchanges signaling carrying weighting informationwith the secondary nodes and the UE for a weighted trafficsplitting/merging at a packet data convergence protocol (PDCP) layer.18. The method of claim 17, wherein the PDCP Protocol Data Units (PDUs)routing/merging occurs for each single uplink radio bearer that isdestined to the MN through one or more nodes.
 19. The method of claim17, wherein the PDCP Protocol Data Units (PDUs) scheduling/splittingoccurs for each single downlink radio bearer that arrives at the UEthrough one or more nodes.
 20. The method of claim 15, wherein theinter-node mobility involves switching between (N−1)-way and N-way ofeach split bearer, wherein N is an integer that is greater than one.